什么是蒸汽喷嘴|蒸汽喷嘴形状的类型

Introduction to Steam Nozzle ;

蒸汽涡轮机转换了由蒸汽发生器产生的高压，高温蒸汽的能量，使其成为轴工作。

A steam nozzle may be defined as不同的横截面的通过，蒸汽的热能通过该传递转化为动能。蒸汽喷嘴的主要功能是生产具有高速度的蒸汽射流以驱动蒸汽涡轮机。

The energy conversion is brought about in the following ways:
1.高压高温蒸汽首先在喷嘴中扩展为高速流体流。
2. The high-velocity steam coming out of the nozzles impinges on the blades mounted on a wheel. The fluid stream suffers a loss of momentum while flowing past the blades that is absorbed by the rotating wheel entailing the production of torque.
3.移动叶片由于蒸汽的冲动而移动（由动量的变化引起），也是由于蒸汽相对于它们的膨胀和加速而移动。换句话说，它们也充当喷嘴。

蒸汽喷嘴是平稳变化的横截面区域的管道或通过，将蒸汽的热能转化为动能。设计喷嘴的形状使其可以以最小的损失执行这种能量转换。

蒸汽喷嘴的工作：

During the first part of the nozzle, the steam increases its velocity. And then the later part of the nozzle, in which the steam derives more in volume than in velocity.

Note:

1.由于通过喷嘴的任何部分的大量蒸汽保持恒定。
2.喷嘴中蒸汽压力的变化取决于蒸汽的速度，比体积和干燥分数。

用途：The main use of a steam nozzle in steam turbines is to produce a jet of steam with a high velocity. The smallest section of the nozzle is called the throat.

喷嘴的类型：

1. Convergent Nozzle
2. Divergent Nozzle
3. Convergent-Divergent Nozzle

收敛喷嘴：

A typical convergent nozzle is shown in fig. in a convergent nozzle, the cross-sectional area decreases continuously from its entrance to exit. It is used in a case where the backpressure is equal to or greater than the critical pressure ratio.

发散喷嘴：

发散喷嘴的横截面区域从其入口到出口不断增加。在这种情况下，这种情况使用，而背压小于临界压力比。

收敛性喷嘴：

在这种情况下，横截面区域首先从喉咙入口减少，然后从喉咙出口增加。它在许多类型的蒸汽轮机中广泛使用。

流通喷嘴

A喷嘴is a duct that increases the velocity of the flowing fluid at the expense of pressure drop.

降低流体速度并导致压力相应增加的导管是扩散器.
The same duct may be either a nozzle or a diffuser depending upon the end conditions across it. If the cross-section of a duct decreases gradually from inlet to exit, the duct is said to be convergent.
相反，如果横截面从入口到出口逐渐增加，则据说该管道是不同的。
If the cross-section initially decreases and then increases, the duct is called a convergent-divergent nozzle.
The minimum cross-section of such ducts is known as the throat.
据说液体是可压缩if its density changes with the change in pressure brought about by the flow
If the density does not change or changes very little, the fluid is said to be in-compressible. Usually the gases and vapors are compressible, whereas liquids are incompressible.

喷嘴的形状

1.在亚音速速度（MA <1）下，该区域的降低会增加流速。
2.在超音速流（MA> 1）中，面积变化的影响不同。

Significance of Mach number –

如果马赫数小于一个，则流量为声音，并且喷嘴是收敛的。
如果马赫数等于1，则流量为声音。
如果马赫数大于一个，则流量为超音速，喷嘴发散。

Nozzle efficiency:

它是有用的热滴与等递热滴的比率。它用k表示

K = Useful Heat Drop / Isentropic Heat Drop

我们如何找到有用的热量下降和等凝热下降，所以让我们讨论一些有用的发现喷嘴效率的有用点？

当蒸汽流过喷嘴时，由于喷嘴表面和流动的蒸汽之间的摩擦，其焓或总热量会损失。最好在H-S图或Mollier图表的帮助下最好地理解这一点，如图所示：

Process of h-s Diagram:

1. First of all, locate the point A for the initial conditions of the steam. It is a point, where the saturation line meets the initial pressure (P1) line.
2. Now draw a vertical line through A to meet the final pressure (P2) line. This is done as the flow through the nozzle is isentropic, which is expressed by a vertical line AB. The heat drop (h1 – h2) is known as the isentropic heat drop.
3.由于喷嘴中的摩擦，蒸汽中的实际热量将小于（H1-H2）。让这种热量显示为AC而不是AB。
4.随着蒸汽在压力P2处的膨胀，因此，通过在C中绘制水平线以满足B’处的最终压力（P2）线，从而获得了蒸汽的最终条件。
5. Now the actual expansion of steam in the nozzle is expressed by the curve AB’ (adiabatic expansion) instead of AB (isentropic expansion). The actual heat drop (h1 – h3) is known as a useful heat drop.

The efficiency of a nozzle generally varies from 0.85 to 0.95.

影响喷嘴效率的因素

1.喷嘴的材料。
2.喷嘴的尺寸和形状。
3.喷嘴完成。
4. Angle of divergence.
5.流体及其状态的性质，
6. Friction.
7.流体速度。
8. Turbulence in the flow passages

喷嘴的选择标准。

Situation first:It is used when the backpressure is equal or more than the critical pressure ratio. It is also used for non – compressible fluids.

收敛喷嘴：从入口到出口，横截面区域连续下降。

Situation second:当背压小于临界压力发散喷嘴时。

Divergent nozzle:Cross-sectional area is increases continuously from entrance to exit.

情况第三：当反向压力小于临界压力收敛性喷嘴时。

收敛性和发散喷嘴：喷嘴的横截面首先连续减少，然后从入口到出口增加。

Application Of Steam Nozzle :

蒸汽和燃气轮机 -
Jet Engine
Rocket Motors-
It is used to measure the discharge of fluid.- e.g. Venturimeter
用于向锅炉喂水的喷油器。
The supersonic gas turbine engine: for the air intake when the air requirement of the engine is high.
Rockets: for providing sufficient thrust to move upwards.
For removing air from the condenser using the injector.
Spray painting
Steam jet refrigeration system